Optically sensitized photographic silver halide emulsions



Sept. 12, 1950 A. w. ANISH 2,521,959

' OPTICALLY SENSITIZED PHOTOGRAPHIC SILVER HALIDE EMULSION Original Filed March 10, 1944 INVENTOR. A/fr'ec/ W 4/1/5/7 Patented Sept. 12, 1950 l OPTICALLY SENSITIZED PHOTOGRAPHIC SILVER HALIDE EMULSIONS Alfred W. Anish, Vestal, N. Y., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware Original application March 10, 1944, Serial No.

525,935, now Patent No. 2,441,342, dated May 4 Claims.

This invention relates to photographic gelatino silver-halide emulsions, and particularly to photographic emulsions sensitized by means of benzoxazole trimethine dye salts having a substitution in the -position of the benzene nucleus Divided and this application August 8, 1947, Serial No. 767,582

Other objects and advantages of this invention will become apparent by reference to the following specification in which the preferred details and embodiments are described.

5 This invention is based onthe discovery that consisting of a branched chain alkyl and a such dyes can be prepared by condensing branched alkyl radical containing an aryl group. 2-methylbenzoxazole quaternary ammonium sensitizing dye salts of the benzoxazole trisalt,'substituted in the 5-position by a branched methine series, which are substituted in the benchain alkyl or a branched chain alkyl radical zene nucleus by a straight chain alkyl, alkoxy, having a aryl group, with ethyl orthoiormate. dialkylamino and hydroxy group are the sub- Such dyes not only cause a shift in the spectral jects of several patents. In all of these dyes, region to longer wave lengths but also give rise however, the substitution in the benzene nucleus to an unexpected higher sensitivity maximum causes a shift in the region of sensitivity toward than the corresponding dyes containing straight the longer wavelength region of the spectrum, chain alkyl or dialkyl groups with a very sharp and also causes a corresponding shift in the limits cut-ofi near the upper limit of sensitization. to which the dye sensitizes. In other words, the Paraphrasing this, an oxacarbocyanine dye, hav entire range of added spectral sensitivity is ing a butyl group attached to the benzene ring, shifted toward the longer Wavelength region by has a fiat sensitivity maximum at a shorter wave any simple straight chain alkyl substitution on length reading, whereas a similar dye, having a the benzene ring. tertiary butyl group attached to the benzene In view of the foregoing facts, the problem ring, has a sharp sensitivity maximum. The net was to provide a benzoxazole, which when coneffect of a straight chain alkyl substitution is to densed with a cyanine dye intermediate, would cause a gradualdecline from sensitivity maxiyield a oxacarbocyanine dye characterized not mum to the limits of sensitization, and the net only by a spectral sensitivity shift toward the eifect in the case of a branched chain alkyl is longer wavelength region of the spectrum, but to cause a sharp decline in sensitivity maxialso characterized by a steep cut-off in the specmum to the limits of sensitization. The latter tral curve for use in silver-halide emulsions for phenomenon is commonly referred to as a sharp color photography, wherein the sensitizing dye sensitivity cut-off. would cause a sharp decline in sensitivity maxi- The sensitizing dyestuffs suitable for the purmum near the upper limit of the sensitization, pose of the present invention are characterized and at the same time would have a more selecby the following general formula: tive response to green light. This sharp cutoff is highly desirable in multi-color photography O 0 where each of the silver-halide emulsions sensitized to the primary colors, viz., blue, green, and 0 CH=CH OH=G red, should be sensitized with a dye giving a minL I R mum overlap of sensitization in the composite layer so as to produce clearer and truer pictures. 40

An object of the present invention is to pro- X vide photographic silver-halide emulsions with benzoxazole trimethine cyanine dyes substituted wherein R represents a branched chain alkyl in the 5-position by a branched chain alkyl and radical or a branched chain alkyl radical conbranched chain alkyl radical having an aryl taining an aryl group such as, for example, isogroup. butyl, cumyl, isoamyl, tertiary amyl, tertiary A further object is to provide such dyes which hexyl, isopropyl, diisobutyl, 2-, or 3-, methylare characterized by a steep cut-oil in the specbutyl groups, R1 and R2 represent an alkyl or tral curve and a more selective response to green aralkyl group, e. g., methyl, ethyl, propyl, butyl, light. benzyl, methylbenzyl, ethylbenzyl, propylbenzyl,

3 4 and the like, and X represents an anion such as, Example I for example, Cl, Br, I, SOziCHs, C104, 1,1'-dietl1yl-6,6'-dicumyloxacarbocyanine iodide moi-4311:

H o H SCN or any other acid radical formlng an 3 C 3 alkyl or aralkyl ester. The benzoxazole intermediates used in the H; N In preparation of the aforesaid dyestuifs are repre- 02115 I (J2EE sented by the following structural formula: 1;} 2.5 grams of 2 methyl e cumylbenzoxazole 0 ethyl p-toluenesulfonate, 1.5 grams of ethyl orthoiormate, and 10.0 cc. of pyridine were refluxed C-CHB for 3 hours. The reaction mixture was then R cooled and poured into 50 cc. of water contain- N ing 1 gram of potassium iodide and allowed to wherein R is of the same value as above. These Stande dye cryst which precipitated, Were intermediates and their salts are prepared acfiltered and Washed with t d fi y recording to the methods set forth in my copendcrystallized from ethyl alcohol. Brilliant yellow, ing application s ri N 525,936, fil d M h flat,prisrn-shaped dye crystals are obtained which 10, 1944, now United States Patent 2,429,178, mel at 270 C. issued October 4, 1947. The corresponding Incorporated in agelatino silver bromide emul- 2 (5 acetanilidovinyl) benzoxazole derivatives SiOH Co taining about .4-.5% of silver iodide, the are prepared according to the methods set forth dye sensitizes from about 490 me to about 560 m in my copending application Serial No. 525,937, with a maximum at about 540 mi, and with a filed March 21, 1947, now United States Patent harp cut-off as shown in Fi ure 2,429,179, issued October 14, 1947.

In preparing the sensitizing dyes utilized in Example H accordance the present invention the fore- 1,1'-dietl1yl-6,6'-ditert.-butyloxacarhocyanine iodide going intermediate, in the form of a quaternary o O ammonium salt, is condensed with ethyl orthoformate under reflux conditions in the presence H30 G GH=GH CH=C on, of a basic (acid binding) condensing agent such ch 9 as pyridine, ethylmethylpyridine, trimethylpyri- H3 N N H dine, quinoline, and the like. The dye salt thus 4 obtained may be, if desired, converted into a a 5 2 difierent salt by treating it in solution with an 2.4 grams each of 2-methyl-6-tert.-butyl-benzaqueous solution of a salt containing the desired oxazole ethyl p-toluenesulfonate and ethyl orthoanion such as, for example, potassium bromide formate were condensed by refluxing in 10.0 cc. or iodide. of pyridine for 2 /2 hours. The cooled reaction The diagrammatic spectograms constituting mixture was poured into water containing three the accompanying drawing, illustrate the regions grams of potassium iodide and allowed to stand.

of the spectrum to which the various dyes, uti- The water was decanted, the residue was washed lized in the present invention, will sensitize a with water followed by ethyl ether and then crysgelatino silver-halide emulsion containing about talllzed twice from ethanol. Red rhombic crys- .&-.5% of silver-iodide and the extent of the sentals are obtained, which melt at 257 C.

sitization at various wavelengths. Incorporated in a gelatino silver bromide emul- The figures of this drawing and the specific sion containing about .4.5% of silver iodide, the type of dyes, the sensitizing properties of which dye sensitizes from about 190 m to about 560 m they illustrate, are as follows: with a maximum at about 535 m and with a Figure 1 shows the sensitivity and the steep 5o sharp cut-ofi as shown in Figure 2.

Example III 1,1-diethyl-6,6'-diisoamy1oxacarbocyanine perchlorate 0 0 CH3 \OOH=OHOH=O/ CH3 CH-OHa-CH OHrCHr-O our N cns v 2 5 C104 zHt cut-off in the spectral curve of the emulsion con- 2.0 grams of 2-methyl-6-isoamylbenzoxazole taining the dye of Example I. ethyl p-toluenesulfonate and 2.0 grams of ethyl Figure 2 shows the sensitivity and the steep orthoformate in 10.0 cc. of pyridine were heated cut -off in the spectral curve of the emulsion conunder reflux for 2 hours. The cooled reaction taining the dye of Example II. mixture was diluted with water and on standing Figure 3 shows the sensitivity and the steep separated as on oil. After repeated washings with cut-off in the spectral curve of the emulsion conwater, the oil was dissolved in alcohol and 10% taining the dye of Example III. of sodium perchlorate solution added. The dye The following examples describe in detail the crystals were separated and recrystallized from methods for accomplishing the above objects, but ethyl alcohol. Red, blue reflex (rhombic) crysit is to be understood that they are inserted merely tals are obtained, which melt at 225 C. for the purpose of illustrations and are not to be Incorporated in a gelatino silver bromide emulconstrued as limiting the scope of the invension containing about .1-.5% of silver iodide, the

tion. dye sensitizes from about 490 my. to about 560 m with a maximum at about 535 m and with a wherein Rrepresents a member selected from the sharp cut-01f as shown in Figure 3. class consisting of a branched chain alkyl radical In the preparation of emulsions containing the and branched chain alkyl radical containing an foregoing dyes, the dyestuif may be dissolved in aryl group, R1 and R2 represent a member selected methyl or ethyl alcohol and a solution thereof 5 from the class consisting of alkyl, and aralkyl containing from 5 to 50 milligrams of the dyegroups, and X represents an anion. stuff added to a liter of emulsion. While in gen- 2. A photographic gelatino-silver-halide emul eral practice it may not be necessary to add the sion which contains a dye of the following strucdyestufi in the amounts larger than those above ture: given, generally, for satisfactory results, amounts usually ranging from 5 to 25 milligrams are sufficient to obtain a maximum sensitizing efiect.

However, I do not wish to limit my invention to H36 CH8 the quantities indicated as the most suitable H C B C H amount will, in each case, be found by a few 5 comparative experiments. The dyestuifs may be HS HE added to the emulsion in the form of a solution. I 2H5 Suitable solvents as previously indicated are the alcohols, for instance, methyl or ethyl alcohol,

whi h may be anhyd u o d l w a Small 3. A photographic gelatino-silver-halide emulv lum of W In actual p a t the dyestuffs sion which contains a dye of the following strucare applied to the emulsion during any stage of burg;

its production, however, they are preferably added to the finished emulsion before being cast.

This application is a division of my copending application Serial No. 525,935, filed March 10, H 0 O CH3 1944, now United States Patent 2,441,342, issued H G i r 0 May 11, 1948. 3 3 "A;

While there have been pointed out above cer- H8 (I; Hi tain preferred embodiments of the invention, the 30 I 2H6 same is not limited to the foregoing examples, illustrations, or to the specific details given therein, but is capable of variations and modifications 4. A photographi gelatino-silver-halide emulas to the reactants, proportions and conditions sion which contains a dye of the following strucemployed, Accordingly, it is intended that the ture: 1

on, N N on: 02 0 \C10| aHa invention be defined only by the accompanying claims. ALFRED W. ANISI-I.

I claim:

1. A photographic gelatino silver-halide emul- REFERENCES CITED sion which contains a compound selected from The following references are of record in the the group consisting of compounds of the general file of this patent: formula:

UNITED STATES PATENTS i Number Name Date C 0H=0H CH=C 2,173,486 Schneider Sept. 19, 1939 R R 2,230,257 Middleton et al Feb. 4, 1941 i 2,233,509 Brooker et al. Mar. 4, 1941 2,323,504 Wilson July 6, 1943 X I 2,354,524 Kumetat et al. July 25, 1944 

1. A PHOTOGRAPHIC GELATINO-SILVER-HALIDE EMULSION WHICH CONTAINS A COMPOUND SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS OF THE GENERAL FORMULA: 